8. Avengers: Endgame
Avengers: Endgame's position within the Marvel Cinematic Universe makes it hard to determine whether or not it's technically a sequel to the other 21 movies that came before it. It doesn't matter though because it is a sequel to The Avengers - and therefore also a sequel to Avengers: Age Of Ultron and Avengers: Infinity War.
The Avengers rounded out the MCU's first phase by bringing all of its major stories together. Six heroes uniting to take on an alien invasion in Manhattan might seem rather tame by later films' standards but it held its own for a number of years, standing alone as the perfect example of how to unite a league of beloved comic book superheroes on the silver screen.
Endgame may have been bigger but that didn't necessarily mean it would be better. After all, Age of Ultron tried that and ultimately failed to surpass its predecessor. Infinity War came close to but where Endgame ultimately succeeded is that it managed to recapture the poignant magic of its equally brilliant predecessor and merge that with the almost epic triumph of the first movie - all while paying tribute to the entirety of the MCU in the process.
It also had the unenviable task of concluding the Avengers saga and the MCU's overarching narrative and it still managed to pull all of it off, giving us a satisfying ending to both.